Waterproof photographic paper and method of making same



Jan. 1, 1957 c, STAEHLE 2,776,236

WATERPROOF PHOTOGRAPHIC PAPER AND METHOD OF MAKING SAME Filed March 19, 1954 HENRY c. s TAEHLE INVENTOR.

TTOR/VEYS BY (5 1M United States Patent WATERPROOF PHOTOGRAPHIC PAPER AND METHOD OF MAKING SAME Henry C. Staehle, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 19, 1954, Serial No. 417,501

11 Claims. (Cl. 154-120) This invention concerns the treatment of paper to improve its water resistance, more particularly the treatment of photographic paper to increase its resistance to aqueous processing solutions.

In the photographic art, various methods have been used in the past to waterproof paper or .to make it water resistant. However, some of these processes have been relatively expensive and are unable to compare favorably in cost to normally used photographic papers even though they result in substantial saving of time and equipment. Moreover, some of the Waterproofing compositions may bleed or leach through into the photographic emulsions causing fog or spots which are objectionable. Consequently, there has been a need for an inexpensive waterproof paper which would cost approximately the same as commercially available photographic papers and Wh1ch would be compatible with photographic emulsion.

Processing photographic prints using paper normally available requires considerable washing and drying inasmuch as the chemicals which are used in photographic processes tend to be absorbed in the photographic paper and must be removed by time consuming washing. Following this extensive washing, it is necessary to dry the prints to remove the water in order to present them in a finished condition. A waterproof paper would not absorb these chemicals from the processing baths, and, therefore, would not require the long wash period or as elaborate washing equipment as is now in use. Moreover, certain photofinishing machines could be redesigned to make them smaller and to process photographic prints in shorter time. One attempt to solve the problem of providing a waterproof paper has been suggested which involves coating the paper with wax which is compatible with photographic emulsions. However, when such a paper is rolled tightly on a drum, the surfaces tend to adhere to each other resulting in blocking of the sheets. Also, when such paper is cut on a paper cutter involving more than a single sheet, the pressure required for the cutting knife may also result in blocking. On the other hand, brittleness must be avoided in photographic paper so that the paper may be rolled for handling. It must also be able to withstand temperature differences so that it may be used in northern climates or in the tropics. I have found a method of waterproofing paper which is compatible with photographic emulsions, and which provides a paper which is able to withstand the rigors of handling under various conditions. Moreover, it appears that this process can be carried out at favorable cost.

An object of this invention is to provide a waterproof paper. Another object of this invention is to provide a method of waterproofing paper. An additional object of this invention is to provide a resin latex coating for photographic paper. A further object is to provide a water resistant photographic paper compatible with a lightsensitive emulsion containing silver salts. Still another object of this invention is to provide a method of water- Proofing P ographic paper which has been baryta coated on both surfaces. Additional objects will be apparent from consideration of this specification.

The accompanying drawing shows diagrammatically the position of the resin coatings on the paper surface.

The above objects are obtained by coating the paper 10 with a binary coating system using two resin dispersions. The first resin dispersion 11 is a soft resin which tends to fill depressions in the paper and prevent the formation of pinholes which might cause defects in the final waterproof condition of the paper. The second coating 12 is a hard resin which is coated over the soft resin coating 11 using a lamination method and resulting in a high gloss photographic paper. The soft resin dispersion 11 is a high polymer latex having about 50% solids content of a copolymer of ethylacrylate and acrylonitrile comprising from 5 to 50% of the latter. This coating is applied as a thin layer onto the paper 10 by means of an airknife, hopper, dip coater, bead coating or other well known coating technique, and thoroughly dried in warm air. The hard resin dispersion 12 is a high polymer latex which contains about 40% solids of an interpolymer comprising from 2 to 20% N-methylmethacrylamide, 40 to 60% n-butylacrylate and 40 to 60 acrylonitrile. It is important in applying the second coating that the paper 10 be laminated to a polished surface, such as a polished chromium drum. After the paper has remained in laminated contact with the polished surface for from about 20 to 40 seconds, the paper is peeled from the surface and dried in warm air.

It will be obvious to one skilled in the art that certain of the above conditions may be varied within the limits of my invention. For instance, the coated paper may be dried at room temperature or with cool air, but this would necessitate a longer period of drying. In my preferred embodiment, I use a soft resin dispersion comprising about ethylacrylate and 25% acrylonitrile and a hard resin dispersion containing about 8% N-methylmethacrylamide, 46% n-butyl acrylate and 46% acrylonitrile.

In order to determine the waterproof conditions of paper coated using my invention, a sample of the dried paper coated according to my preferred embodiment was tested by immersing a section for at least one minute in a strong solution of Rhodamine dye containing as a surface active agent, Triton N-lOO, which is an aryl alkyl polyether alcohol. The absence of pinholes was apparent since the dye layer was easily removed in running water. This test is used to indicate the presence of pinholes which would be penetrated by the dye.

I have found that the nature of the solvent added to the resin dispersion is extremely important. Ethylene chloride is the preferred solvent but other solvents such as ethyl acetate and benzol may be used. If a solvent such as trichloroethylene is used with the resin coating, too elastic, a film is formed, and at the time of pulling the sheet from the polished surface, the resin coating will pull away from the paper surface in a spotty fashion to produce an unsatisfactory coating. On the other hand, the use of a solvent such as chloroform tends to produce a coating which is not sufficiently waterproof and which will absorb Rhodamine dye when tested as above.

I- claim:

1. A waterproof paper having a binary coating, a first coat comprising a copolymer of ethyl acrylate and acrylonitrile and a second coat comprising an interpolymer of N-methyl methacrylamide, N-butyl acrylate and acrylonitrile.

2. A waterproof paper according to claim 1 in which the copolymer used in the first coat contains 5095% by weight ethyl acrylate and the interpolymer used in the second coat contains from 2 to 20% by weight N-methyl 3 methacrylamide, 40-60% by weight N-butyl acrylate and 40-60% by weight acrylonitrile.

3. A Waterproof photographic paper according to claim 2 in which the paper has been baryta coated on both sides prior to the application of the Waterproof coating.

4. A method for applying a waterproof coating on paper comprising coating the paper with a resin dispersion containing a copolymer of ethyl acrylate and acrylonitrile, drying, and coating with a second coat containing an interpolymer of Nrnethyl methacrylamide, N-butyl acrylate and acrylonitrile.

5. A method of waterproofing photographic paper with a binary coating system comprising coating the paper with a first coat containing a copolymer of from 50-95% ethyl acrylate and 5-50% acrylonitrile, drying, coating with :1 second coat containing an interpolymer of from 2-2064) N-methyl methacrylamide, 40-60% N-butyl acrylate and 40-60% acrylonitrile.

6. A process according to claim 5 in which the paper is contacted against a polished metal surface immediately following the second coating operation, and separated therefrom after contacting for 20-40 seconds.

7. in a process for waterproofing paper using a binary coating system, the step which comprises applying a first coat having about 50% solids content of a copolymer comprising about 75% ethyl acrylate and about 25% acrylonitrile.

8. In a method for waterproofing photographic paper using a binary coating system, a step comprising applying a second coat comprising about 40% solids of an interpolymer containing about 8% N-butyl methacrylamide, about 46% N-butyl acrylate and about 46% acrylonitrile.

9. A process according to claim 8 in which the paper is contacted against a polished surface immediately following coating with the resin dispersion, permitted to remain in contact with the polished surface for from 20-40 seconds, separated therefrom and dried.

10. A process according to claim 9 in which the resin dispersion coating is carried in a solvent selected from the class consisting of ethylene chloride, bcnzol, and ethyl acetate.

11. A process according to claim 7 in which the resin dispersion coating is carried in a solvent selected from the class consisting of ethylene chloride, ethyl acetate and benzol.

References Cited in the file of this patent UNITED STATES PATENTS 450,963 Kuhn Apr. 21, 1891 1,751,882 Pifer Mar. 25, 1930 2,273,880 Mitchell Feb. 24, 1942 2,276,244 Fisher et al Mar. 10, 1942 2,392,972 Cheyney Jan. 15, 1946 2,571,725 Kimball et a1. Oct. 16, 1951 

1. A WATERPROOF PAPER HAVING A BINARY COATING, A FIRST COAT COMPRISING A COPOLYMER OF ETHYL ACRYLATE AND ACRYLONITRILE AND A SECOND COAT COMPRISING AN INTERPOLYMER OF N-METHYL METHACRYLAMIDE, N-BUTYL ACRYLATE AND ACRYLONITRILE. 